pr90
A meteor stream is composed of dust particles that have been ejected from a parent comet at a variety of velocities. These particles follow the same orbit as the parent comet, but due to their differing velocities they slowly gain on or fall behind the disintegrating comet until a shroud of dust surrounds the entire cometary orbit. Astronomers have hypothesized that a meteor stream should broaden with time as the dust particles' individual orbits are perturbed by planetary gravitational fields. A recent computer-modeling experiment tested this hypothesis by tracking the influence of planetary gravitation over a projected 5,000-year period on the positions of a group of hypothetical dust particles. In the model, the particles were randomly distributed throughout a computer simulation of the orbit of an actual meteor stream, the Geminid. The researcher found, as expected, that the computer-model stream broadened with time. Conventional theories, however, predicted that the distribution of particles would be increasingly dense toward the center of a meteor stream. Surprisingly, the computer-model meteor stream gradually came to resemble a thick-walled, hollow pipe.
Whenever the Earth passes through a meteor stream, a meteor shower occurs. Moving at a little over 1,500,000 miles per day around its orbit, the Earth would take, on average, just over a day to cross the hollow, computer-model Geminid stream if the stream were 5,000 years old. Two brief periods of peak meteor activity during the shower would be observed, one as the Earth entered the thick-walled "pipe" and one as it exited. There is no reason why the Earth should always pass through the stream's exact center, so the time interval between the two bursts of activity would vary from one year to the next.
Has the predicted twin-peaked activity been observed for the actual yearly Geminid meteor shower? The Geminid data between 1970 and 1979 shows just such a bifurcation, a secondary burst of meteor activity being clearly visible at an average of 19 hours (1,200,000 miles) after the first burst. The time intervals between the bursts suggest the actual Geminid stream is about 3,000 years old.
1.The primary focus of the passage is on which of the following?
(A) Comparing two scientific theories and contrasting the predictions that each would make concerning a natural phenomenon
(B) Describing a new theoretical model and noting that it explains the nature of observations made of a particular natural phenomenon
(C) Evaluating the results of a particular scientific experiment and suggesting further areas for research
(D) Explaining how two different natural phenomena are related and demonstrating a way to measure them
(E) Analyzing recent data derived from observations of an actual phenomenon and constructing a model to explain the data
This question asks you to identify the primary focus of the passage. The best answer is the second choice. The author describes the new theoretical model in the first paragraph; in the final paragraph the author states that the data obtained from actual observations, which are discussed in the second and third paragraphs, is consistent with the new theoretical model.
The first choice is not correct; the computer model confirmed the astronomers' hypothesis that meteor streams broaden with time.
The third choice is also incorrect. Although the model yielded an unexpected result, the passage makes no reference to further areas for research.
The fourth choice incorrectly mentions two natural phenomena. Although the passage does mention two natural phenomena—a meteor stream and planetary gravitation—it focuses on only a single phenomenon, the meteor stream; there is mention that meteor streams are affected by planetary gravitation, but there is no explanation of how they relate, nor any demonstration of how to measure the phenomena themselves.
The last choice is not correct because it reverses the order of events. The model yielded a prediction that was subsequently confirmed by observational data; the model was not constructed to explain the data.
2. According to the passage, which of the following is an accurate statement concerning meteor streams?
(A) Meteor streams and comets start out with similar orbits, but only those of meteor streams are perturbed by planetary gravitation.
(B) Meteor streams grow as dust particles are attracted by the gravitational fields of comets.
(C) Meteor streams are composed of dust particles derived from comets.
(D) Comets may be composed of several kinds of materials, while meteor streams consist only of large dust particles.
(E) Once formed, meteor streams hasten the further disintegration of comets.
3. The author states that the research described in the first paragraph was undertaken in order to
(A) determine the age of an actual meteor stream
(B) identify the various structural features of meteor streams
(C) explore the nature of a particularly interesting meteor stream
(D) test the hypothesis that meteor streams become broader as they age
(E) show that a computer model could help in explaining actual astronomical data
4. Q. It can be inferred from the passage that which of the following would most probably be observed during the Earth's passage through a meteor stream if the conventional theories mentioned in line 18 were correct?
(A) Meteor activity would gradually increase to a single, intense peak, and then gradually decline.
(B) Meteor activity would be steady throughout the period of the meteor shower.
(C) Meteor activity would rise to a peak at the beginning and at the end of the meteor shower.
(D) Random bursts of very high meteor activity would be interspersed with periods of very little activity.
(E) In years in which the Earth passed through only the outer areas of a meteor stream, meteor activity would be absent.
5. According to the passage, why do the dust particles in a meteor stream eventually surround a comet’s original orbit?
(A) They are ejected by the comet at differing velocities.
(B) Their orbits are uncontrolled by planetary gravitational fields.
(C) They become part of the meteor stream at different times.
(D) Their velocity slows over time.
(E) Their ejection velocity is slower than that of the comet.
6. The passage suggests that which of the following is a prediction concerning meteor streams that can be derived from both the conventional theories mentioned in line 18 and the new computer-derived theory?
(A) Dust particles in a meteor stream will usually be distributed evenly throughout any cross section of the stream.
(B) The orbits of most meteor streams should cross the orbit of the Earth at some point and give rise to a meteor shower.
(C) Over time the distribution of dust in a meteor stream will usually become denser at the outside edges of the stream than at the center.
(D) Meteor showers caused by older meteor streams should be, on average, longer in duration than those caused by very young meteor streams.
(E) The individual dust particles in older meteor streams should be, on average, smaller than those that compose younger meteor streams.
7. It can be inferred from the last paragraph of the passage that which of the following must be true of the Earth as it orbits the Sun?
(A) Most meteor streams it encounters are more than 2,000 years old.
(B) When passing through a meteor stream, it usually passes near to the stream’s center.
(C) It crosses the Geminid meteor stream once every year.
(D) It usually takes over a day to cross the actual Geminid meteor stream.
(E) It accounts for most of the gravitational perturbation affecting the Geminid meteor stream.
8. Which of the following is an assumption underlying the last sentence of the passage?
(A) In each of the years between 1970 and 1979, the Earth took exactly 19 hours to cross the Geminid meteor stream.
(B) The comet associated with the Geminid meteor stream has totally disintegrated.
(C) The Geminid meteor stream should continue to exist for at least 5,000 years.
(D) The Geminid meteor stream has not broadened as rapidly as the conventional theories would have predicted.
(E) The computer-model Geminid meteor stream provides an accurate representation of the development of the actual Geminid stream.
1. The primary focus of the passage is on which of the following?
(A) Comparing two scientific theories and contrasting the predictions that each would make concerning a natural phenomenon
….incorrect, this passage doesn’t compare two scientific theories
(B) Describing a new theoretical model and noting that it explains the nature of observations made of a particular natural phenomenon
….correct
…..at first I just think option(B) only partially correct, this is only about the former half of para1
SEE para1
……In the model, the particles were randomly distributed throughout a computer simulation of the orbit of an actual meteor stream….
…..“Conventional theories”( not new theoretical model), however, predicted that the distribution of particles would be increasingly dense toward the center of a meteor stream.
However “I DIDN’T NOTICE THE LATER HALF OF OPTION(B)”, which accurately describes para2&3---meteor shower
(C) Evaluating the results of a particular scientific experiment and suggesting further areas for research
….incorrect, here we doesn’t evaluate anything
(D) Explaining how two different natural phenomena are related and demonstrating a way to measure them
….incorrect
This is an option which I thought is right at first
Whenever the Earth passes through a meteor stream, a meteor shower occurs.
----para2 is about natural phenomena
Para1 is about the introduction to meteor stream(a natural phenomena) and its movement led to the argument of new computer-model
Para2 insert “meteor shower” into para1’s view of “meteor stream”, though we can say para1&2 are both related, but the passage’s main focus doesn’t about how two phenomena related
The Geminid data between 1970 and 1979 shows just such a
bifurcation, a secondary burst of meteor activity being clearly
visible at an average of 19 hours (1,200,000 miles) after the first
burst. The time intervals between the bursts suggest the actual
Geminid stream is about 3,000 years old.
---- demonstrating a way to measure “them”, here the passage
only measure para2&3 rather than para1
(E) Analyzing recent data derived from observations of an actual phenomenon and constructing a model to explain the data
---only partially correct, here in the passage we analyze data both computer modeling as well as actual phenomenon
2. According to the passage, which of the following is an accurate statement concerning meteor streams?
A meteor stream is composed of dust particles that have been ejected from a parent comet at a variety of velocities. These particles follow the same orbit as the parent comet, but due to their differing velocities they slowly gain on or fall behind the disintegrating comet until a shroud of dust surrounds the entire cometary orbit. Astronomers have hypothesized that a meteor stream should broaden with time as the dust particles' individual orbits are perturbed by planetary gravitational fields.
(A) Meteor streams and comets start out with similar orbits, but only those of meteor streams are perturbed by planetary gravitation.
…incorrect
At first I choose this choice and cannot quite understand why its wrong
Its that, if you reason back from (C) could we understand the theorem behind
----if “Meteor streams are composed of dust particles derived from comets.”
----as the author mention in the passage that “meteor streams are perturbed by planetary gravitation.”
----generally speaking, comets will also perturbed by planetary gravitation.”
(B) Meteor streams grow as dust particles are attracted by the gravitational fields of comets.
para1
Astronomers have hypothesized that a meteor stream should broaden with time as the dust particles' “individual orbits” are perturbed by planetary gravitational fields.
notice the difference between sentence in para1 and the statement of (B), though they’re very similar, the sentence clearly indicates its dust particles’ “individual orbits” will influence the “planetary” gravitational field rather than “comet’s”
(C) Meteor streams are composed of dust particles derived from comets.
….correct
sentence in para1 clearly correspond to the statement of (C)
A meteor stream is composed of dust particles that have been ejected from a parent comet at a variety of velocities.
(D) Comets may be composed of several kinds of materials, while meteor streams consist only of large dust particles.
the article doesn’t hint anything about the composition of comet and meteor stream
(E) Once formed, meteor streams hasten the further disintegration of comets.
nowhere in the article mention the “hasten of the further disintegration of comets”
3. The author states that the research described in the first paragraph was undertaken in order to
(A) determine the age of an actual meteor stream
Its para2&3, not para1
(B) identify the various structural features of meteor streams
(C) explore the nature of a particularly interesting meteor stream
(D) test the hypothesis that meteor streams become broader as they age
….correct
(E) show that a computer model could help in explaining actual astronomical data
4. Q. It can be inferred from the passage that which of the following would most probably be observed during the Earth's passage through a meteor stream if the conventional theories mentioned in line 18 were correct?
Conventional theories, however, predicted that the distribution of particles would be increasingly dense toward the center of a meteor stream. Surprisingly, the computer-model meteor stream gradually came to resemble a thick-walled, hollow pipe.
(A) Meteor activity would gradually increase to a single, intense peak, and then gradually decline.
….correct
Below is the new computerized model’s view, opposite to conventional one
Two brief periods of peak meteor activity during the shower would be observed, one as the Earth entered the thick-walled "pipe" and one as it exited.
(B) Meteor activity would be steady throughout the period of the meteor shower.
(C) Meteor activity would rise to a peak at the beginning and at the end of the meteor shower.
(D) Random bursts of very high meteor activity would be interspersed with periods of very little activity.
(E) In years in which the Earth passed through only the outer areas of a meteor stream, meteor activity would be absent.
5. According to the passage, why do the dust particles in a meteor stream eventually surround a comet’s original orbit?
(A) They are ejected by the comet at differing velocities.
….correct
A meteor stream is composed of dust particles that have been ejected from a parent comet at a variety of velocities. These particles follow the same orbit as the parent comet, but due to their differing velocities they slowly gain on or fall behind the disintegrating comet until a shroud of dust surrounds the entire cometary orbit.
(B) Their orbits are uncontrolled by planetary gravitational fields.
(C) They become part of the meteor stream at different times.
(D) Their velocity slows over time.
(E) Their ejection velocity is slower than that of the comet.
6. The passage suggests that which of the following is a prediction concerning meteor streams that can be derived from both the conventional theories mentioned in line 18 and the new computer-derived theory?
(A) Dust particles in a meteor stream will usually be distributed evenly throughout any cross section of the stream.
both theories does not think particles “be distributed evenly throughout any cross section of the stream”
(B) The orbits of most meteor streams should cross the orbit of the Earth at some point and give rise to a meteor shower.
????
Whenever the Earth passes through a meteor stream, a meteor shower occurs.
(C) Over time the distribution of dust in a meteor stream will usually become denser at the outside edges of the stream than at the center.
Only new computer-model rather than conventional theories
(D) Meteor showers caused by older meteor streams should be, on average, longer in duration than those caused by very young meteor streams.
….correct
(E) The individual dust particles in older meteor streams should be, on average, smaller than those that compose younger meteor streams.
….out of scope
7. It can be inferred from the last paragraph of the passage that which of the following must be true of the Earth as it orbits the Sun?
On new computer-model’s side
Has the predicted twin-peaked activity been observed for the actual yearly Geminid meteor shower? The Geminid data between 1970 and 1979 shows just such a bifurcation, a secondary burst of meteor activity being clearly visible at an average of 19 hours (1,200,000 miles) after the first burst. The time intervals between the bursts suggest the actual Geminid stream is about 3,000 years old.
(A) Most meteor streams it encounters are more than 2,000 years old.
…..incorrect
Most meteor streams(this paragraph only talks about Geminid stream) it encounters are more than 2,000 years old.
(B) When passing through a meteor stream, it usually passes near to the stream’s center.
(C) It crosses the Geminid meteor stream once every year.
….correct
Thus we can infer the meteor stream’s age
(D) It usually takes over a day to cross the actual Geminid meteor stream.
….incorrect
…but it also can be 19 hrs or others
(E) It accounts for most of the gravitational perturbation affecting the Geminid meteor stream.
8. Which of the following is an assumption underlying the last sentence of the passage?
Has the predicted twin-peaked activity been observed for the actual yearly Geminid meteor shower? The Geminid data between 1970 and 1979 shows just such a bifurcation, a secondary burst of meteor activity being clearly visible at an average of 19 hours (1,200,000 miles) after the first burst. “The time intervals between the bursts suggest the actual Geminid stream is about 3,000 years old.”
(A) In each of the years between 1970 and 1979, the Earth took exactly 19 hours to cross the Geminid meteor stream.
…incorrect
The Geminid data between 1970 and 1979 shows just such a bifurcation, a secondary burst of meteor activity being clearly visible at an average of 19 hours (1,200,000 miles) after the first burst.
Every year between 1970-1979, “all exactly 19hrs”…..wrong
--we only know “average”, but we cannot say “all exactly 19hrs”, its too overgenerializtion
(B) The comet associated with the Geminid meteor stream has totally disintegrated.
….out of scope
(C) The Geminid meteor stream should continue to exist for at least 5,000 years.
….out of scope
(D) The Geminid meteor stream has not broadened as rapidly as the conventional theories would have predicted.
….incorrect
Here we’re not concerned with the rate of broadening
(E) The computer-model Geminid meteor stream provides an accurate representation of the development of the actual Geminid stream.
….correct
THIS IS A VERY TOUGH PASSAGE, if you're not major in astronological, you cannot quit grasp, in a very short time, the whole picture of what this passage really talks about, I try to use picture-visual rather than words to present this passage's idea by drawing a sketch attached below
Attachments
pic.docx [28.51 KiB]
Downloaded 68 times

DSC_0250.JPG [ 4.79 MiB | Viewed 10821 times ]